Electro-optic animated displays and indicators

ABSTRACT

In this invention, animation effects have been obtained in a device containing a light source illuminating a linear polarizer producing plane polarized light which is rotated in an electro-optical cell/cells such as a Liquid Crystal or PLZT cell. The angle of the plane is changed at the required speed by a voltage applied to the electrodes of the cell; this voltage being generated in an electronic circuit or obtained from the output of a transducer or manually. The rotated plane polarized light is shining through a stationary set of at least two linear polarizers oriented at different angles and then through a screen containing the art work. The emerging lighted image is perceived by the viewer as a change or as an animated movement of the art work. Color effects can also be obtained when a chromatic polarizer or a chromatic retardation plate is used. In the prior art, the change of the angle of the plane polarized light was achieved by mounting the linear polarizer on a mechanically rotated wheel. The introduction of electro-optical voltage controlled cells has many advantages such as speed of response, illumination of moving parts, feasibility of new effects, and flexibility of design. The applications of this invention are in advertising and exhibition displays, animated signage, animated printed material, instrument readout indicators and monitors, works of art, and in the field of toys and games.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to animated displays and used in advertising,merchandising, instructional and educational fields. It is related todisplays using light polarisation effects in order to illustratemovement of various objects, flow of liquids or flow of energy insystems that are graphically or artistically depicted on a backlightedor frontlighted screen or are projected on a separate screen. Theanimation effects can include linear, curved, wavelike, rotational,pulsating, accelerating, decelerating, blinking and the like effects andthe effects can be limited to the parts on the display screen to beanimated. This invention also relates to means of selectivelyilluminating limited areas on a dark screen such as used, for example,in indicators, signals and advertising panels. Information in forms ofpictures, artwork symbols, letters, alphanumerics that is fixed orchanged as a function of a measured quantity can form a part of ananimated display or form a separate display device such as an indicator,meter or monitor of any physical quantity that may or may not include ananimated arrow or other picture to draw attention. This invention alsorelates to colored displays animated and/or stationary in which thecolor or color change is obtained through the interaction of polarisedlight with a chromatic polariser.

2) Description of Prior Art

The now commercially available polarising mosaic is defined next for thepurpose of describing and claiming the invention. The preferreddefinition is an assembly of achromatic or chromatic linear polarisersegments having different angles of polarisation placed in the sameplane that forms one sheet by suitable bonding techniques. In analternative form know in the art and commercially available, asdisclosed in the book by W. A. Shurcliffe entitled: "Polarised Light",Harvard University, 1962 and in the patent by A. Siksal Can. 778 075granted on Feb. 13, 1968 such segments can be embossed on a plasticsheet, thus modifying the birefringence, dichroism or chromaticity ofthese sheets, which, when bonded to another polariser sheet fulfills thesame function with the same results as the assembly of polarisersegments.

In the prior art animated displays of the type outlined in the foregoinghave been generally characterised by the presence of a a lights source,a rotable polariser, manually or motor driven and a polarising mosaic asdefined above. One such display device is disclosed in the patent to D.N. Yates U.S. Pat. No. 3,054,204 granted on Sept. 18, 1962 and another,which might be considered an improvement on the former, is disclosed inthe patent to A. Siksal, cited. Both show a motor driven polariser discbeing an integral and necessary part of the system. In the prior artdevices capable of selectively illuminating parts of a dark screen,using the light polarisation phenomena applied to indicators oradvertising panels, also relied on rotating parts as disclosed forexample in the patent to J. F. Dreyer, Can. 496 723 issued Oct. 8, 1953.In the prior art production of animated color effects or selectivelyilluminated colored parts on the viewing screen has been obtained byplacing suitably oriented and shaped birefringent or dichroic plasticmaterial between two polarisers (the second being often referred as theanalyser), one of them being usually a motor driven polariser disc. Anexample of such a display is disclosed in the patent to F. Burchell U.S.Pat. No. 2,393,968 granted on February, 1946.

The presence of mechanical often motor driven parts in the prior artdisplays and indicators discussed in the foregoing gives rise to anumber of undesirable side effects. In addition to wear and tear, thatcalls for regular maintenance, it is necessary to control some noise,vibration and heat generation due to the operation of an electric motor.Also, since a rotating disc is usually circular in shape and the displaypanel usually square or rectangular, a common problem arising is that ofilluminating the corners and edges of the panel with rotating polarisedlight. Additional pulleys and discs have to be provided for the corners;they do not solve the problem completely and add to the complexity ofthe design. Although the speed of the motor is controllable, it cannotbe changed quickly enough to produce certain desired animation effects.The range of possible animation effects could be greatly enlarged andthe process could be simplified were it possible to animate individuallythe desired Portions of the display. However the speed of the motor insuch displays often determines the rate of change of the animationeffects throughout the whole display panel. The above mentionedlimitations of prior art devices can be overcome and a number ofadvantages and new animation effects can be realised by the presentinvention. They will be explained in the parts of the specifications tofollow.

SUMMARY OF THE INVENTION

I have found that certain recently perfected electro-optic devices offera practical solution for the elimination of the mechanical elements inanimated display panels and in indicators and can be also adapted toproduce color effects. It has been known for a long time that certainsolids, liquids and gases rotate the plane of polarisation whensubjected to high electric or magnetic fields. The electro-opticaleffects have been known as the Kerr and Pockels effect and themagneto-optical effects have been known as the Cotton-Moutton and theFaraday Effect. Unfortunately the devices based on these effects wereusually bulky, required high electric or magnetic fields and weregenerally not practical for use in display panels. It was only duringthe last ten years that concentrated R and D effort all over the worldled to inexpensive, thin, transparent devices capable of rotating theplane of polarisation, which are suitable for flat display panels. Thesedevices will be referred to in the following as polarotator cells. Theyare well summarised in the book "Flat-Panel Displays and CRT's" by E.Lawrence and Tannas Jr., Van Nostrand Reinhold Co. New York, 1985.

Of the possible electro-optical devices capable of rotating the plane ofpolarisation it has been found that a suitably modified Twisted NematicLiquid Crystal cell and PLZT Ferroelectric Ceramic cell both beingtransparent, were very suitable for use is such displays. A thin filmiron-garnet cell might be also suitable. To date such cells have beenused mostly in watches, computer and instrument displays. They operatein a mode in which the angle of the plane of linearly polarised light isbeing switched from zero to 90 or more degrees and back with thetransition period between the two angles being very short although notwidely known and explained in the literature on the subject (M. Schadtand W. Heiflich, Applied Physics Letters, vol. 18, No. 4, pp. 127-128,Feb. 15, 1971) . It will be appreciated that any angle can be obtainedand maintained between the zero and maximum angle and that the angle canbe changed and controlled by the voltage applied to the electrodes ofthese cells. It has been found that most animation effects that wereobtained with a mechanically rotating polariser disc can be alsoobtained by placing such cells over the areas or details of the paneldesign to be animated in conjunction with a polarising mosaic. In caseswhere a 360 degree rotation of the polarisation plane is required, todepict for example the rotational movement of a wheel, an assembly oftwo to four such cells or a single cell energised by a suitably shapedvoltage can accomplish this task as will be explained in greater detailin the following.

It will be apparent to a person skilled in the art that all of thepreviously mentioned drawbacks of mechanical elements will be eliminatedusing such electro-optical devices. In addition, distinct advantageswill become apparent such as complete freedom with regard to theplacement of the animated details on the panel, including the cornersand edges. Each detail could be animated from a separate electroniccircuit at its own rate and speed or can be stationary or slowlychanging to supply information only. Thus new effects and effectdistribution and control, until now not possible, can be realised bysuch electro-optical means. These and other desirable objects andproperties of the invention will become evident to a person skilled inthe art as they are discussed in the following specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings which illustrate the principles of the embodiments of theinvention, may be modified and changed as regards the immediateillustration, all within the true intent and scope of the invention,hereinafter defined and claimed.

FIG. 1 is one embodiment of the invention for an animated or indicatordisplay, showing diagrammatically a cross section of such a display, inwhich the location of the polariser and polarising mosaic could beinterchanged.

FIG. 2 shows the plane view of the functional structure of a polarisingmosaic to produce the impression of a linear movement or flow.

FIG. 3 shows a plane view of a polarising mosaic to produce a rotaryspoke wheel effect.

FIG. 4 shows a plane view of a polarising mosaic to produce a bull eyeeffect of radially expanding or contracting form.

FIG. 5 show a plane view of a polarising mosaic to produce anaccelerating motion effect.

FIG. 6 shows a plane view of a polarising mosaic to produce a checkerboard effect.

FIG. 7 shows a plane view of a polarising mosaic in an embodiment for anindicator where the polarising mosaic has the shape of numbers.

FIG. 8 shows typical relationship between the angle α of rotation of theplane of polarisation of a polarotator cell and the voltage applied toits electrodes.

FIG. 9 shows examples of waveforms of the voltage applied to theelectrodes of the polarotator cell in order to produce an animatedeffect.

FIG. 10 shows a cross section of an example of a device consisting of upto four polarotator cells to produce up to 360 degree rotation of theplane of polarisation.

FIG. 11 shows the initial angular alignment and the change of thepolarisation angle α as a function of time of the four cells in FIG. 10when connected in series.

FIG. 12 shows an embodiment of the invention shown in FIG. 1 in anadaptation for viewing in reflected light.

FIG. 13 shows an embodiment of the invention shown in FIG. 1 in anembodiment for viewing and animating an illustration on a page.

FIG. 14 shows an embodiment of the invention to produce independentlycontrolled animation and color effects using two polarotator cells and achromatic polariser.

FIG. 15 shows an embodiment of the invention as in FIG. 14 but using achromatic linear retarder.

The above shown embodiments of the invention and its details basicallyinvolve the combination of an liquid crystal, PLZT ceramic, thin filmiron garnet cell or other suitable polarotator cell and a polarisingmosaic to produce an animated movement or flow effect or to produce aselectively illuminated indicator effect. The various forms of thepolarising mosaic shown in FIGS. 2, 3, 4, 5, 6 and 7 and many other formare well known in the art are described in detail in the patents by D.M. Yates and A. Siksal cited, and are available commercially, forexample from Polaroid and Frank Woodlley Co. Inc. They have been shownhere in order to assist in the description of the invention. The liquidcrystal and PLZT polarotator cells are also well known in the art. Theyhave been perfected recently and are available commercially for examplefrom the Crystalaid and UCE Company and Motorola Company respectively.The combination of the electronic voltage waveform generator circuit,the polarotator cells and polarising mosaic is believed to be novel andit results in an improved and simplified animated display device. Theoperation of such a device and some of its possible variations andmodifications will be now described in greater detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic embodiment of the invention is shown diagrammatically inFIG. 1. Refinements of design which might be required, such as forexample an enclosure, a protective plastic or glass light directing ormodifying means such like, lenses or light diffusers or absorbers andthe like, will be evident to people skilled in the art and they are notshown for the sake of clarity. The embodiment consists of a uniformsuitable incandescent, fluorescent or natural light source (4) with orwithout a light diffuser, the light source being plane polarised in thelinear polariser (3) and the angle of the plane being rotated in thepolarotator cell (2) by an angle which depends on the voltage generatedin an electronic circuit transducer or manually using for example avariac or potentiometer (8) and applied to the transparent electrodes(6) deposited on or attached to the walls of the cell. The cell could bepreferably a Twisted Nematic Liquid Crystal cell or a PLZT FerroelectricCeramic shutter cell, having the top and bottom polariser removed. Theglass or plastic transparent image screen (7), with a picture artwork,graphics or alphanumerics being applied suitably on it, is placed on thecell. The polarising mosaic (1) as defined in the foregoing is bonded bysuitable means to at least part of the inside of the image screen, overthose portions of the picture details only which have to be animated. Itis noted that the location at the polariser and the polarising mosaiccould be interchanged to obtain the same result. The picture is beingseen by the observer (5) from above or from the side if the device isplaced vertically. The configuration as described together with thelight source is enclosed in a suitable box designed to be eitherstationary or portable or equipped if required with means to interchangethe image screen with the polarising mosaic bonded onto it. Referring toFIG. 2 observe the vertical strips a,b,c,d, of the polariser mosaicsegments sequentially assembled at progressively increasing polarisingangles, side by side and repeating the same angular sequence in thestrips e,f,g,h and the strips i,j,k,l. Depending on the angle of theplane of polarised light emerging from the polarotator cell and passingthrough the polarising mosaic, the strips having the same angle willtransmit the light and those at 90 degrees to the angle of the planewill block the light. Strips that are oriented at intermediate angleswill show progressively darkening shades of gray. The correspondingdetails of the picture on the image screen will exhibit then the samelight distribution. FIG. 8 shows the shape of the curve describing therelationship between the angle α of rotation of the plane ofpolarisation emerging from the polarotator cell and the voltage appliedto its electrodes. Note, that at voltage V₁ the angle is almost zero andat the voltage V₂ almost 90 degrees. The typical voltages for theTwisted Nematic and the PLZT cells are approximately V₁ =3 volts and 110volts and V₂ =5.5 volts and 160 volts respectively. If one arranges forexample the angles of the strips a and d, e and h and i and L in FIG. 2to differ by 90 degrees, the strips a,e and i will light up at thevoltage V₁, the strips d, h and L at the voltage V₂ and the other stripswill light up at the voltages between. The voltage could be made to varyin a saw-tooth manner between V₁ and V₂ as shown in FIG. 9a, using wellknown electronic circuit techniques. Then as the voltage increases fromV₁ towards V₂ successive strips will be illuminated creating theimpression of a wave-like movement of shades of light from the "a" tothe "d", the "h" and to the L strip. As these strips are attached to theimage screens the corresponding movement of the picture detail, forexample the flow of fluid will be seen. The return from the voltage V₂back to V₁ is designed to be very fast so that the successive cyclesmerge together to create a continuous movement. The speed of themovement, determined by the period T can be controlled electronicallyover a wide range. A variety of wave forms, other than saw-tooth, suchas square, and triangular shown in FIGS. 9b and 9c and many otherwaveforms can be easily generated using electronic circuits well knownto the art. Then a corresponding variety of animation effects can beobtained. For example the triangular waveform with the mosaic shown inFIG. 2 will give rise to a linear pulsating movement. In addition,depending on the sequence, the placement and the size of the segmentsother effects can be realised as illustrated in FIG. 3 to FIG. 7. Usingthe saw-tooth waveform, examination of the polarising mosaic of FIG. 3reveals to a person skilled in the art that a rotary spoke-wheel effectwill be obtained with such segment assembly, that of FIG. 4 will give aradially moving motion, that of FIG. 5 an accelerating movement effect,and that of FIG. 6 an alternating blinking checkerboard effect. Othereffects can be obtained using other waveforms.

Polarotator cells as described permit a rotation of the plane ofpolarisation by almost 90 degrees. Although the majority of animationeffects can be accomplished with a single cell and using suitably shapedvoltages there may be situations where a specific effect requires arotation of 180, 270 or 360 degrees. A further embodiment of theinvention accomplishes this using two, three or four polarotator cellsrespectively, one behind the other as shown in FIG. 10. In such anarrangement each successive cell is turned first by 90 degrees usingsuitable alignment techniques known to the art when connected in seriesvoltage waveforms are shaped to rotate the angle α of the plane ofpolarisation in each cell to produce an angle-time relationship shown inFIG. 11. The numbers in FIG. 10 indicate the same components as the samenumbers in FIG. 1. The electronic circuit transducer or manual voltagecontroller (8) is designed to provide two, three or four outputs ofsuitable shaped voltages. The spacings between the four cells are shownfor the sake of clarity and can be eliminated providing a propertransparent insulation. Further simplification in construction can beobtained by combining the two adjacent walls of each two neighboringcells into a single wall spacer. Thus for example in the case of LiquidCrystal cell such single glass spacer wall will be coated on both sideswith transparent electrode material.

A further embodiment of the invention relates to stationary or changingpatterns such as used in indicators or meters of a physical quantitybeing measured or monitored. They can be also obtained using theconfigurations described in the foregoing. In FIG. 7 an example of anindicator is shown where the indicia were cut out of a polarising sheetand placed at progressively increasing polarisation angles for theseries of numbers. A number will light up for a given measured quantitysince the angle is related to the voltage which in turn is related tothe measured or monitored quantity using transducers well known in theart. This configuration represents a very inexpensive method toconstruct a monitor or meter display or an indicator. An animated arrowor picture could be added to such an indicator to draw attention to arange of numbers representing for example a zone of danger. It will beevident to a person skilled in the art that a large variety of displaydevices can be constructed, based on the above principles. Such deviceswould also include toys and games where the voltage is obtained from atransducer or a manually operated voltage controller, such as apotentiometer or variac.

FIG. 12 shows the embodiment of the invention when the light source (4)is on the side of the observer (5) and an opaque or semi-transparent areflector which may also comprise means to enhance, spectrally modify ofdiffuse the incident light such as a suitably treated white paper orfluorescent or colored metal foil (9) is placed below the polariser (3)replacing or complementing the light source (4) in FIG. 1. All theeffects described in the foregoing can be then observed in reflection.This is because polarisation of light is not lost as a result ofreflection. This mode of operation might be advantageous in certainsituations such as when viewing in daylight and in suitably illuminatedrooms or when it is preferable to illuminate the panel from the outside.A still further embodiment of the invention in the reflection viewingmode relates to animating an illustration or a picture of a printed pagesuch as in an educational book and is shown in FIG. 13. The picture tobe animated is printed or coated on a transparent screen (11) made ofplastic or glass. The polarising mosaic (10) is bonded to the screen andto the reflecting page (12). The observer (17) is looking through adevice shaped to be placed over the eyes or shaped as a hand held device(15) which contains the polarotator cell (18), with its transparentelectrodes (19) and the attached polariser (13) and a solid stateminiature electronic circuit transducer or manual voltage controller(14) energising the cell (18). Such a device is illuminated either fromdaylight or artificial light source (16) which can be separate orattached to the device. Note that such a device is separated from thepicture carrying page and is placed away from it at a distance foundmost suitable for viewing under the given light conditions. Theelectronic circuit can generate several waveforms that are selected forthe type of animations required for the picture being viewed.

In a still further embodiment of the invention shown in FIG. 1 simplemodifications permit large scale projection of the animated picture. Thesource of light (4) is replaced by projection lamps to permit projectionon a large screen for mass audience viewing. Means are provided toenable easy interchanging or replacement of the picture screen(7) havingthe polarising mosaic segments (1) bonded to the details of the pictureto be animated.

In a still further embodiment of the invention two polarotator cells areused in combination with chromatic, sometime referred to as spectralpolariser or in combination with a chromatic linear retarder, well knownin the art (see book by W. A. Shurcliffe, cited) which are commerciallyavailable. This permits independent and separate production and controlof color effects and animation effects. In FIG. 14 the upper portion ofsuch an embodiment produces the animation effects and consists of thepicture carrying screen (26) polarising mosaic (25), polarotator cell(20) with its transparent electrodes (27), energised and controlled fromthe output (a) of the electronic circuit transducer or manual voltagecontroller (29). This upper portion receives plane polarised coloredlight from the chromatic or spectral polariser (23) but its function isidentical to the basic embodiment shown in FIG. 1. The chromaticpolariser (23) may represent a dyed linear polariser which absorbs apart of the visible spectrum and thus produces colored light istransmission. In such a case the change of angle of the plane ofpolarised achromatic light entering such polariser from the secondpolarotator cell (21), with its transparent coated electrodes 28, andpolariser (24) changes the saturation of the transmitted colored light.The degree of saturation can be controlled electronically from theoutput (b) of the electronic circuit transducer or manual voltagecontroller (29). The chromatic polariser may also consist, of twocommercially available dyed linear polarisers, say one passing bluelight and the other red light, bonded together with their polarisationaxis at 90 degrees to each other and forming one sheet. In such a casethe change of angle of the plane of polarised achromatic light enteringthis polariser from the polarotator cell (21) oriented at 45 degrees tothe axis of the former changes the hue. The hue of the colored light canbe thus controlled from the output (b) of the electronic circuittransducer or manual voltage controller (29).

In FIG. 15 independent control of animation effects and control of hueof the emerging colored light can be obtained in a similar manner as inFIG. 14. However change of hue is obtained from the interaction of thepolariser (34) and the chromatic linear retarder (35) with the change ofangle of the plane polarised achromatic light as it emerges from thepolarotator cell (33); the latter housing the coated transparentelectrodes (40) and an attached polariser (36). The output (a) of theelectronic circuit transducer or manual voltage controller (41) controlsthe animation effects as in the basic embodiment of FIG. 1, and theoutput (b) controls thus the hue of the emerging colored light. Theremaining parts (42), (32), (37), (38) and (43) are similar to thecorresponding parts in FIG. 14 explained before. A further method ofcontrolling the colour of the emerging light is by substituting thechromatic linear retarder by one or more layers of a birefringement film(such as polyvinyl alcohol film or cellulose films or polyvinyl fluoridefilm). It will be appreciated that a serial assembly of the arrangementsdescribed in the foregoing to control either the saturation or have ofthe colour will result in the control of both. It is evident to a personskilled in the art that the embodiments shown in FIG. 14 and FIG. 15 canbe adapted to viewing an illustration on a page or to viewing inreflected light or in the application as an indicator following theprinciples shown in FIG. 13, FIG. 12 and FIG. 7 respectively.

While the preferred embodiments of the inventions have been explainedand illustrated it will be appreciated that the invention is notrestricted to these specific forms but it may consist of furtherembodiments and is of broader scope as defined in the claims. Inparticular, as shown in FIGS. 14 and 15 and depending on theapplication, the upper part of the device that produces animation can beused separately or it can be used on conjunction with the lower partthat produces colour effects.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A display devicecomprisingi) a light source; ii) a linear polariser for plane polarisinglight from said source; iii) at least one first electro-optical cellcapable of changing the angle of the plane of polarisation of polarisedlight emerging from said polariser; iv) at least one layer of achromatic polariser; v) at least one second electro-optical cell capableof changing the angle of the plane of polarisation of the colouredpolarised light emerging from said chromatic polariser; vi) at least onelayer mosaic of light polarising means consisting of at least two parts,each part oriented in a different direction of polarisation, located tobe illuminated by coloured polarised light emerging from said secondelectro-optical cell; vii) a transparent viewing screen carryinginformation located to be illuminated by said light source directly orfrom said second cell and said mosaic; said second cell and said mosaicilluminating at least a part of said screen; viii) means of generating avoltage or voltage waveforms for changing and controlling the angle ofpolarisation of at least one said cell (iii), and (v), thereby alsocontrolling the pattern and colour of light emerging from said mosaic(vi) which in turn illuminates said information on said screen (vii). 2.A display device as described in claim 1, wherein said polarisers, saidcells, said mosaic, said screen is a thin layer with an exterior surfacefacing toward a viewer, when the device is in its operative position,and an interior surface facing away from a viewer when said device is inits operative position.
 3. A display device as described in claim 2,further comprising an opaque or semi-transparent light reflector forreflecting, enhancing, spectrally modifying or diffusing the saidincident light, said reflector having a reflecting exterior surfacefacing towards the viewer, parallel to the interior most surface of saiddevice facing away from the viewer.
 4. A display device described inclaim 3, wherein the location of one of said polarisers and said mosaicare interchanged.
 5. A display device as described in claim 4, whereinsaid device is in two discrete parts, said linear polariser, chromaticpolariser, at least one said electro-optical cell, said means ofgenerating a voltage or voltage waveforms being the first part, and saidmosaic, screen and reflector being a second part; the viewer views saidsecond part through said first part.
 6. A display device as described inclaim 2, wherein said linear polariser, chromatic polariser, at leastone said electro-optical cell, mosaic, screen and said means ofgenerating a voltage or voltage waveforms are formed as part of aprojection device and a projection lamp is provided to illuminate theinterior most side of the device in lieu of the light source.
 7. Adisplay device as described in claim 1 or 3 or 5 or 6, in which the saidfirst cell and said second cell are capable of rotating the angle of theplane of polarisation of polarised light to any value in the range of atleast from about 0 to about 90 degrees, depending on the voltage appliedthereto.
 8. A display device as described in claim 7, comprising anadditional similar cell added to the second cell, the additional cellcapable of rotating the angle of polarisation of polarised light by atleast from about 0 to at least 90 degrees, depending on the voltageapplied thereto, said additional cell having interior and exteriorsurfaces parallel to those of the second cell, the two cells produce anapparent rotation of the angle of polarisation by at least from aboutzero to about 180 degrees.
 9. A display device as described in claim 8,comprising a further additional similar cell capable of rotating theangle of polarisation of polarised light by at least from about 0 to 90degrees, depending on the voltage applied therein, said furtheradditional cell having interior and exterior surfaces parallel to thoseof the second cell, the three cells to produce an apparent rotation ofthe angle of polarisation by at least from about zero to about 270degrees.
 10. A display device as described in claim 9, comprising astill further additional similar cell capable of rotating the angle ofpolarisation of polarised light by at least from about 0 to 90 degreesdepending on the voltage applied thereto, said still further additionalcell having interior and exterior surfaces parallel to those of thesecond cell, the four cells to produce an apparent rotation of the angleof polarisation by at least from about zero to about 360 degrees.
 11. Adisplay device as described in claim 7, wherein at least one saidelectro-optical cell is a liquid crystal cell.
 12. A display device asdescribed in claim 11, wherein at least one said electro-optical cell isa twisted nematic liquid crystal cell.
 13. A display device as describedin claim 7, wherein at least one said electro-optical cell is aferroelectric cell.
 14. A display device as described in claim 7,wherein at least one said electro-optical cell is a PLZT ceramic cell.15. A display device as described in claim 7, wherein at least one saidelectro-optical cell is a thin-film iron garnet cell.
 16. A displaydevice as described in claim 12, wherein said means of generating avoltage or voltage waveforms are an electronic circuit, transducer or amanual voltage controller the output of which is connected to said cellsby means of transparent electrodes spread across and covering at least apart of some of the surfaces of said cells.
 17. A display device asdescribed in claim 12, wherein the chromatic polariser is a dyedachromatic polariser which determines the colour saturation of the lightemerging from said first cell.
 18. A display device as described inclaim 12, wherein said chromatic polariser is comprised of twodifferently dyed polarisers having their optical axis offset by about 90degrees from each other and by 45 degrees from the optical axis of theinterior most linear polariser of said device, whereby the saidadditional cell will determine the hue of the coloured light emergingtherefrom.
 19. A display device as described in claim 12, wherein saidchromatic polariser is comprised of a chromatic linear retarder and alinear polariser.
 20. A display device as described in claim 12, whereinsaid chromatic polariser is comprised of at least one layer of atransparent birefringent film and a linear polariser.
 21. A displaydevice as described in claim 12, wherein said display device forms atleast a part of a painting, sign, an advertising or exhibition display.22. A display device described in claim 5, wherein said display deviceis formed to animate printed material.
 23. A display device as describedin claim 12, wherein said display device is formed to be an instrumentreadout indicator.
 24. A display device as described in claim 12,wherein said display device forms at least a part of a toy or game.